A method to calculate mobilities of ions in gas mixtures

Takata, N.

doi:10.1088/0022-3727/18/9/010

Cited by 11 publications

(8 citation statements)

References 9 publications

(8 reference statements)

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“…The disparity in properties between He and CO 2 challenge the assumption that fully elastic collisions between an ion and neutral are occurring to ensure the validity of Blanc’s law. Takata makes a similar conclusion in observing deviations from Blanc’s law in mixtures of H 2 /N 2 , where he states that the deviations stem from inelastic collisions, especially at high E/N values . Due to the observed deviation from Blanc’s law for the He/CO 2 mixture, AAA was not tested for that mixture of gases.…”

Section: Resultsmentioning

confidence: 87%

“…Takata makes a similar conclusion in observing deviations from Blanc's law in mixtures of H 2 /N 2 , where he states that the deviations stem from inelastic collisions, especially at high E/N values. 30 Due to the observed deviation from Blanc's law for the He/CO 2 mixture, AAA was not tested for that mixture of gases.…”

Section: ■ Resultsmentioning

confidence: 99%

“…Additional efforts were made in the mid-20th century to further characterize Blanc’s law as more IMS theory was being developed. Numerous studies have been conducted to characterize the possible deviations from Blanc’s law over the years, including in the case of temperature, electric field, , kinetic theory, and the identity of the analyte, including electrons. − Notably, for this work, Patterson describes how the mobilities of a limited set of negative-mode ions adhere to the hard-sphere models and the polarization limit for Blanc’s law . However, all of these early attempts to characterize Blanc’s law were performed using a binary mixture of (mostly) atomic drift gases to analyze atomic cations in the presence of an electric field. ,,, To update the assumptions that Blanc’s law is completely accurate with the only exceptions being chemical reactions occurring with the drift gas, binary mixtures of various drift gases were used with polyatomic IMS standards to reflect the predominant use of contemporary analytes (e.g., polyatomic and multiply charged analytes).…”

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confidence: 99%

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Assessing the Impact of Drift Gas Polarizability in Polyatomic Ion Mobility Experiments

2020

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Due to the core assumptions of kinetic theory and the drive toward realizing reproducible gas-phase measurements, ion mobility experiments are commonly conducted in the presence of an inert, neat buffer gas, usually nitrogen or helium. Mixing drift gases in defined, static ratios can provide useful information not only for optimizing the separation of analytes but also for defining the interaction between the ion and neutral particle. In a foundational effort, we seek to validate the role of the drift gas polarizability on the observed mobility of the ions by systematically mixing drift gases to discretely access a range of bulk gas polarizabilities not given by pure drift gases. Compared to historical efforts to probe the role of polarizability on the ion−neutral collisional cross section where a linear relationship was assumed, the data collected in the present effort clearly illustrate a quadratic dependency of the ion−neutral particle collision cross section and polarizability (R 2 > 0.999). When translating these data into the mobility dimension, we illustrate that the gas-phase mobility of polyatomic ions conforms to Blanc's law. These observations combined with considerations related to Langevin's polarization limit provide an experimental mechanism to estimate to what degree an ion−neutral interaction conforms to either the hard-sphere or induced-dipole model. To support these observations, additional comparisons are made with the respective reduced masses, polarizabilities, and mobilities of ions in mixtures where different degrees of hard-sphere interactions are present.

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Section: Resultsmentioning

confidence: 87%

Section: ■ Resultsmentioning

confidence: 99%

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confidence: 99%

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Assessing the Impact of Drift Gas Polarizability in Polyatomic Ion Mobility Experiments

2020

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“…As H 2 molecules ( M = 2 Da) have half the mass of He, the mobilities of large ions with the same Ω in H 2 are 2 1/2 = 1.41 times those in He. While early fundamental studies of the mobilities for the smallest ions included H 2 and its mixtures, − analytical IMS has not and no cross sections of larger ions with H 2 have been measured. These should somewhat exceed Ω with He because diatomic H 2 is larger and more polarizable (α = 0.82 Å 3 ), resulting in deeper ion–molecule potentials.…”

Section: Fundamentals Of Resolving Power For Faims Employing Hydrogenmentioning

confidence: 99%

Accelerated High-Resolution Differential Ion Mobility Separations Using Hydrogen

2011

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The resolving power of differential ion mobility spectrometry (FAIMS) was dramatically increased recently by carrier gases comprising up to 75% He or various vapors, enabling many new applications. However, the need for resolution of complex mixtures is virtually open-ended and many topical analyses demand yet finer separations. Also, the resolving power gains are often at the expense of speed, in particular making high-resolution FAIMS incompatible with online liquid-phase separations. Here, we report FAIMS employing hydrogen, specifically in mixtures with N2 containing up to 90% H2. Such compositions raise the mobilities of all ions and thus the resolving power beyond that previously feasible, while avoiding the electrical breakdown inevitable in He-rich mixtures. The increases in resolving power and ensuing peak resolution are especially significant at H2 fractions above ~50%. Higher resolution can be exchanged for acceleration of the analyses by up to ~4 times, at least. For more mobile species such as multiply-charged peptides, this exchange is presently forced by the constraints of existing FAIMS devices, but future designs optimized for H2 should consistently improve resolution for all analytes.

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“…22 Reasons for these deviations may be attributed to the higher E/N values in a TIMS (45−85 Td), 53 as previous deviations from Blanc's Law up to 4% in the midfield E/N domain have been reported by Milloy and Robson, whereas Takata reports deviation of up to 6% as E/N increases up to 100 Td. 4,54 Once the calibration step was applied (Figure 3B) and a TIMS calibration curve was generated for each gas mixture, the deviations in the elution voltage domain were corrected through the calibration process that converts elution voltage into a mobility value. The deviations from eq 3 are corrected, even though each gas mixture deviates by differing percentages, because a new calibration equation must be calculated for each distinct gas mixture.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Implications of Blanc’s Law for Use in Trapped Ion Mobility Spectrometry

Naylor

Reinecke

Ridgeway

et al. 2021

J. Am. Soc. Mass Spectrom.

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Blanc’s Law has served as a way to predict the mobilities of ions in mixed drift gases for over 100 years yet has remained largely unexplored using newer ion mobility spectrometry (IMS) configurations, including traveling wave and trapped IMS (TIMS) systems. Here, we evaluate a drift-tube IMS (DTIMS) and compare it to a similar set of experiments performed in TIMS. We found that Blanc’s Law can be applied in a DTIMS to determine the mobility of an analyte in the minor gas component of a ternary mixed drift gas system within 2% error. Additionally, the calibration procedure for TIMS to convert elution voltages into a mobility value corrects for significant deviations (>4%) from Blanc’s Law in the elution voltage domain. For the range of gas identities probed in this effort, up to an 11% error in calibrated mobilities was observed when using a gas mixture in the TIMS that differed from the gas used for the reference mobility. However, when the gas mixture within the TIMS was the same as the respective calibrant mobilities, calibration errors within the TIMS were as low as 0.01%. Interestingly, when probing the behavior of ions with argon-containing mixtures within the TIMS, the current accepted paradigm of elution voltage being proportional to inverse mobilities in TIMS calibrations procedures was shown to deviate substantially from the trends observed with DTIMS measurements. With this initial effort, foundations for future mixed drift gas measurements in TIMS are set for expanded analyte classes and larger molecules.

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A method to calculate mobilities of ions in gas mixtures

Cited by 11 publications

References 9 publications

Assessing the Impact of Drift Gas Polarizability in Polyatomic Ion Mobility Experiments

Assessing the Impact of Drift Gas Polarizability in Polyatomic Ion Mobility Experiments

Accelerated High-Resolution Differential Ion Mobility Separations Using Hydrogen

Implications of Blanc’s Law for Use in Trapped Ion Mobility Spectrometry

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